In radiotherapy, heavy ion (heavy particle) radiotherapy, and the like, a lesion is treated by irradiating it with radiation or heavy ion radiation, thereby destroying the lesion. When performing radiotherapy or heavy ion radiotherapy, it is difficult to achieve effective treatment effect unless the radiation or heavy ion radiation is irradiated precisely on the lesion. For this reason, CT (computed tomography) is used to image the target of the treatment (for example, the object to be treated) to gain an understanding of the position of the lesion in three dimensions. A physician or technician determines a treatment plan that includes the angle and radiation strength of irradiation of radiation or heavy ion radiation, based on the determined three-dimensional position of the lesion. When actual treatment is done, positioning is performed to align the position of the object to be treated at the time of treatment with the position of the object to be treated at the time the treatment plan was determined. Because treatment is performed a plurality of times based on the treatment plan, positioning is performed each time. It is necessary that the object to be treated maintains its attitude from the start of the positioning to the end of the treatment, so that it is desirable that the positioning be performed in a short period of time. However, because the positioning must be done precisely, it may be difficult to perform positioning in a short period of time.